docs: add TODO.md from the 6 Oct audit (verified findings)

TODO.md

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+# TODO — Wings of the 90s
+
+Working notes from the 6 Oct 2026 audit. Everything below was measured by running the
+code, not inferred from the README. Upstream: `mac-ai-playground/retro-flight-sim`
+(read-only for `kevinhermes`); work happens in this fork.
+
+## Status check (verified)
+
+- `npm install` + `npm run build` — clean, 13 modules, 512 kB bundle, 581 ms.
+- `npm test` — passes, but see T4: it only counts braces.
+- Terrain is deterministic across instances (`getHeightAt(317,-812)` identical in two
+  separate `Terrain` objects) — the "persistent world" claim holds.
+- Rendering **not** visually verified: the audit box has no GPU and SwiftShader crashes
+  the page. Needs a run on real hardware.
+
+---
+
+## T1 — Takeoff does not work (highest priority)
+
+Simulated 40 s at full throttle against the real `Terrain` heightmap:
+
+| t (s) | knots | alt (ft) | onGround |
+|------:|------:|---------:|:--------:|
+| 0 | 0.3 | 19.7 | false |
+| 1 | 23.2 | 2.8 | false |
+| 2 | 49.3 | 0 | true |
+| 6 | 340.2 | 12.2 | false |
+| 9 | 542.5 | 105.2 | false |
+| 10 | 564.6 | 0 | true |
+| 39 | 2,543.3 | 0 | true |
+
+The aircraft becomes briefly airborne, then never leaves the ground and accelerates to
+Mach 4.1. Causes:
+
+- `js/flight-model.js:77` — ground friction is `-hSpeed * 20`, i.e. 20 N per m/s,
+  against `maxThrust = 50000` N on a 1200 kg airframe. Friction loses every argument.
+- `js/flight-model.js:60-64` — lift is applied while `onGround`, scaled only by
+  `GROUND_LIFT_REDUCTION`, so the plane floats off the runway at arbitrary speed and
+  then the ground-collision clamp at `:95` slams it back down.
+- No weight-on-wheels state: `onGround` is a position test, not a contact state, so
+  there is no normal force and no way to model a proper rotation/tail-up.
+- `PITCH_LIMIT = 85°` and the auto-levelling at `:134-135` (`x *= 0.995`, `z *= 0.985`)
+  fight the player continuously.
+
+**Acceptance criteria:** full throttle from rest → airborne within a plausible
+takeoff roll (order 200–400 m), climb sustained, stall if nose raised too high, and
+speed bounded near a sane VMO instead of 2,500 kt.
+
+## T2 — No WebGL fallback
+
+`js/main.js:36-43` constructs `THREE.WebGLRenderer` with no try/catch. On a machine
+without WebGL the page throws an uncaught `Error creating WebGL context` and the loading
+screen never advances — a blank screen with no message.
+
+**Fix:** wrap renderer init, show a period-appropriate failure card ("GRAPHICS CARD NOT
+DETECTED"), and keep the loading/menu screens usable without 3D.
+
+## T3 — Stall speed is defined but unused
+
+`STALL_SPEED = 25` (`js/flight-model.js:4`) is used only to scale lift. Nothing in
+`hud.js` or `sound.js` references stalling. A period-accurate sim of this era should
+shove a warning in your face.
+
+**Fix:** stall flag on the flight model → HUD warning + stick shaker / audio cue.
+
+## T4 — The test suite is theatre
+
+`scripts/check-syntax.js` checks that each file is >10 chars and that `{` and `}` counts
+match. It cannot catch T1. CI (`.gitea/workflows/*.yml`) runs it on every push, so the
+green tick currently means nothing.
+
+**Fix:** real unit tests on `FlightModel` (takeoff profile, stall, ground contact) and
+`Terrain` (determinism, airport flattening radius). Node has `node:test` built in — no
+new dependency needed. Add a headless smoke test that asserts the game reaches the
+`FLIGHT` state.
+
+## T5 — No LICENSE
+
+README and repo carry no licence. Decide one (MIT matches the sibling `wings88`) and add
+the file.
+
+## T6 — No save/load
+
+The sibling project's brief promised persistent worlds. There is no persistence here —
+no `localStorage`, no world seed stored. Terrain is deterministic per process, which is
+not the same thing.
+
+**Fix:** persist the world seed + aircraft state; add a save/load menu entry.
+
+## T7 — Minor / housekeeping
+
+- `index.html` requests `/favicon.ico` → 404 on every load. Add one, or drop the request.
+- Bundle is 512 kB (132 kB gzipped); Vite warns about the 500 kB chunk. Fine for now,
+  worth a `manualChunks` split if it grows.
+- `package-lock.json` is 31 kB for a two-dependency project — expected, just noting it.
+- No FPS cap. The README brags about a retro feel; `wings88`'s design notes suggest a
+  configurable 20 FPS cap, which would be cheap to add and very on-theme.
+
+---
+
+## Suggested order
+
+T1 → T4 (tests first would be better, but T1 is the reason the project is worth keeping)
+→ T2 → T3 → T5 → T6 → T7.
+
+## Notes on provenance
+
+Two commits, both authored by `mac-container-dev` on 5 May 2026. Not a fork of `wings88`
+(`fork: false`, no cross-references in code) — an independent take on the same brief.
+`wings88` has 214 source lines and no Three.js usage at all; its useful parts are the
+Jest/Playwright setup and the design guidelines (16–32 colour palette, no anti-aliasing,
+20 FPS cap), which would slot in here.